Unlike primary batteries which cannot be recharged, secondary batteries can be repeatedly charged and discharged. Low capacity batteries that use single battery cells are used as power sources for various portable electronic devices such as cellular phones, notebook computers, and camcorders. High power batteries that use tens of battery cells connected to each other in a battery pack are used as power sources for hybrid electric vehicles (HEV).
Secondary batteries are classified according to their external shape into cylinders, prisms, or pouches.
Secondary batteries generally include an electrode assembly which is formed by spirally winding positive and negative electrodes and a separator into a jelly-roll shape. The separator is positioned between the positive and negative electrodes and serves as an insulator. The electrode assembly may alternatively be formed by stacking a positive plate, a negative plate and a separator in a case, and closing the case with a cap assembly. The cap assembly has an external terminal.
The structure of an electrode assembly of a prismatic secondary battery is described in Japanese Unexamined Patent Application Publication Nos. 2000-40501, and 2001-38475, the entire contents of which are incorporated herein by reference.
However, in such a prismatic secondary battery, the electrical connection between the electrode assembly and the external terminal is weak and can be damaged by external impact. The connection is weak because the lead connector connected to the external terminal is welded to an uncoated region of the electrode assembly and positioned in the case without protection.
A secondary battery for a hybrid electric vehicle must have a stable connection in order to output high power. However, when the above described secondary battery is exposed to an external impact such as vibration, a stable connection is difficult to manufacture.